It will indeed be an odd coupling: Keith Lockhart, the handsome, dashing conductor of the Boston Pops Orchestra, and Jack Klugman, the rumpled actor best known for his role as the rumpled slob Oscar Madison on the sitcom The Odd Couple. On Sunday, the 83-year-old Klugman will serve as guest conductor for the annual Pops By the Sea concert, with Lockhart at the musical helm.